As network technology and topology evolve, some users have a need for the new architectures, while at the same time retaining their established networks for economic and other reasons. For example, some companies have extensive investments in subarea networks. Subarea networks are a mainstay of the System Network Architecture (SNA) and are described in detail in many publications and books, such as "SNA: IBM's Networking Solution", James Martin, Prentice- Hall, 1987. Subarea networks are characterized by a topology in which many subarea domains may be interconnected in many ways and in which a domain typically will comprise a hierarchically structured set of nodes. These nodes typically include a host node (a type 5 node in the SNA definition) controlling a tree of other nodes such as communication controllers (type 4 nodes), cluster controllers (type 2 nodes) and end units (type 2 or 1 nodes).
Many of the companies with present or future subarea networks may also direct some of their growth toward peer-to-peer networks (PPNs). PPNs are characterized by a topologically flat interconnection of network nodes, each of which serve a plurality of end nodes. One such PPN network is described in detail in U.S. Pat. No. 4,914,571, which issued on Apr. 3, 1990 to Baratz et al.
In many cases, there is a great need for companies to combine these architecturally different networks into a single logical network from the users point of view. Heretofore, success has been achieved in interfacing networks of like architecture. This has been accomplished, for example, by performing network name and address translation at interface nodes between the networks to avoid the problems of duplicate resource naming in the separate networks. The problem is generally discussed in Chapter 12 of the aforementioned book by Martin. U.S. Pat. No. 4,677,588, which issued to Benjamin et al on Jun. 30, 1987, discloses the details of a solution to the problem of duplicate resource names in combined networks. In view of the teaching of U.S. Pat. No. 4,677,588, searching of combined architecturally similar networks to locate a resource whose location is unknown to a requesting node presents no severe additional problems, because each of the individual networks are of similar architecture and the search algorithms in the networks are the same. However, when architecturally different networks are combined at an interface node, problems arise in the efficient location of resources in the combined network because of the different architectures and search algorithms. For example, if a search request for a resource that originates in the PPN side of a combined PPN/subarea network is merely broadcast into the subarea side from an interface node, all kinds of network havoc may occur. This may be caused in part by an uncontrolled massive search of all subareas and the attending large amount of resulting network traffic. The problem is exacerbated by the possibility of circuitous loops and other problems if multiple interface nodes interconnect the different physical networks or if multiple PPN and/or subarea networks are combined, rather than one of each. Similar problems can occur for a search originating from the subarea network into the PPN side.